guys.. guys.. do not mistake the kernel read ahead with the disk's... the harddisk contains a buffer (256k in mine and 1 mb in the newer models).. when a read request is issued to the disk, the disks logic decides which sectors to 'buffer'... this data is stored in the HDs internal buffer.. and not transferred to the system's memory.. the disk's read ahead and is not controlled but the OS. the kernel has its own buffers to store IO. The kernel would be left to decide which sectors to read into these regions. If the process is IO bound and is reading a file, the kernel can predict the next read and 'prepare' for it (look into inode entries and determine where the next data recides) before the actual read call occurs. This is the kernels readahead. Ideally, they shouldn't be disabled. I have got some of the best performance with full utilization of my disk capabilities.. but don't have a clue on which algorithmn the kernel uses.. but this is twisting the matters a little.. but the bottom line is: hdparam is different from what the kernel does.. DO NOT mistake them > hdparm -A 0 /dev/hda > > man hdparm for more information. > > Amit > > > John Tyner wrote: > > isn't this an option to the hdparm utility? > > > > ----- Original Message ----- > > From: "Zou Min" <zoum@comp.nus.edu.sg> > > To: "Kernelnewbie ML" <kernelnewbies@nl.linux.org> > > Sent: Thursday, April 11, 2002 8:15 PM > > Subject: turning off readahead > > > > > > > >>Hi, > >> > >>I am wondering is there any fast way to disable > the readahead > >>(i.e. prefetching) pages/blocks from disk in 2.4.x > kernel? > >> > >>Thanks! > >> > >>-- > >>regards, > >> > >>ZM > >> > >>-- > >>Kernelnewbies: Help each other learn about the > Linux kernel. > >>Archive: > http://mail.nl.linux.org/kernelnewbies/ > >>FAQ: http://kernelnewbies.org/faq/ > >> > > > > > > -- > > Kernelnewbies: Help each other learn about the > Linux kernel. > > Archive: > http://mail.nl.linux.org/kernelnewbies/ > > FAQ: http://kernelnewbies.org/faq/ > > > > > -- > Kernelnewbies: Help each other learn about the Linux > kernel. > Archive: > http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ > ===== -Sharath __________________________________________________ Do You Yahoo!? Yahoo! Tax Center - online filing with TurboTax http://taxes.yahoo.com/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
